Conventional integrated electronics make use of electrical charge to produce electronic signal processing. Gates control electrical carriers, i.e., holes or electrons in semiconductor devices. Semiconductor devices remain the basis for electronics devices.
Optoelectronic circuits offer the opportunity to make use of the speed of optical signal communication. Optical communications are also less likely to be influenced by interference than electrical signal communications. Typically, optoelectronics finds use in signal communication, such as in optical fiber networks. Optical communications are also used, for example, to communicate information between devices, such as optical communications used in providing audio signals between components in home theatre systems. In conventional optoelectronic devices and systems, interconnects between electronic circuits and optical transceivers are required. Optical signals are not directly processed, but instead are produced when the electrical signals are converted and vice versa.
Conventional optoelectronic devices are based upon a mutual relation between optical absorption or emission and photocurrent or electric field. This is used in some devices to create electrical current in response to absorbed photons, e.g., in photo sensors. This is also the basis for emission of photons in response to applied energy, which is the basis for semi-conductor lasers, light emitting diodes and other devices.
An exciton is a bound state of an electron and a hole, it is, a Coulomb correlated electron-hole pair. An exciton can be formed in a semiconductor when a photon is absorbed. Lifetimes and energy of excitons has been an area of research for a significant time both in quantum well and bulk semiconductor materials.
Coupled quantum well structures have been used to realize indirect excitons composed of electros and holes in separated layers. Lifetimes and energies of excitons in coupled quantum well structures can be controlled, for example, by the application of an electric field. A review of the past work on excitons in coupled quantum wells including the studies of lifetimes and energies of excitons can be found in “Condensation and Pattern Formation in Cold Exciton Gases in Coupled Quantum Wells”, L.V. Butov, J. Phys.: Condens. Matter 16 (2004) R1577-R1613.
The present inventor has previously demonstrated control of indirect exciton energy and overlap between the electron and hole wave functions, which results to change of the absorption and emission rate, by applying voltage to a gate over the entire area of the coupled quantum well planar semiconductor structure. The exciton and electron spin relaxation rates were predicted to be determined by the overlap between the electron and hole wave functions in M. Z. Maialle, E. A. de Andrada e Silva, and L. J. Sham, Phys. Rev. B 47, 15776 (1993). As an example, a change of the exciton-emission rate by about 104 times, which should result to a change of the time of exciton spin flip between optically active spin states by 108 times, as well as a change of the exciton energy by about 40 meV at gate voltage V=1.6 V were demonstrated in Butov et al., “Photoluminescence Kinetics of Indirect Excitons in GaAs/AlGaAs Coupled Quantum Wells,” Phys. Rev. B 59, 1625 (1999).
The electric field in the z direction has been controlled by an external gate voltage Vg applied over an area of the semiconductor materials including a coupled quantum well. At low Vg (direct regime), the spatially direct exciton is the lowest energy state, while at high Vg (indirect regime) the indirect exciton composed of electron and hole in different layers is the lowest energy state. The transition from the direct to the indirect regimes is determined by the ratio between the one-particle symmetric-antisymmetric splittings and the exciton binding energies. For a given coupled quantum well sample, this ratio and the direct-to-indirect crossover can be controlled by magnetic fields. See, Butov, et al. “Direct and indirect magnetoexcitons in symmetric InGaAs/GaAs coupled quantum wells,” Phys. Rev. B 52, 12153 (1995). Butov, et al, “Magneto-optics of the spatially separated electron and hole layers in GaAs/AlGaAs coupled quantum wells,” Phys. Rev. B 60, 8753 (1999).